/*
 * Copyright 2002-2009 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package net.hasor.jdbc.core.mapper;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import net.hasor.jdbc.RowMapper;
import net.hasor.jdbc.core.JdbcTemplate;
import net.hasor.jdbc.core.util.JdbcUtils;
import net.hasor.jdbc.core.util.NumberUtils;
import net.hasor.jdbc.exceptions.InvalidDataAccessException;
import net.hasor.jdbc.exceptions.TypeMismatchDataAccessException;
/**
 * {@link RowMapper} implementation that converts a single column into a single
 * result value per row. Expects to operate on a <code>java.sql.ResultSet</code>
 * that just contains a single column.
 *
 * <p>The type of the result value for each row can be specified. The value
 * for the single column will be extracted from the <code>ResultSet</code>
 * and converted into the specified target type.
 *
 * @author Juergen Hoeller
 * @since 1.2
 * @see JdbcTemplate#queryForList(String, Class)
 * @see JdbcTemplate#queryForObject(String, Class)
 */
public class SingleColumnRowMapper<T> implements RowMapper<T> {
    private Class<T> requiredType;
    /**
     * Create a new SingleColumnRowMapper.
     * @see #setRequiredType
     */
    public SingleColumnRowMapper() {}
    /**
     * Create a new SingleColumnRowMapper.
     * @param requiredType the type that each result object is expected to match
     */
    public SingleColumnRowMapper(Class<T> requiredType) {
        this.requiredType = requiredType;
    }
    /**
     * Set the type that each result object is expected to match.
     * <p>If not specified, the column value will be exposed as
     * returned by the JDBC driver.
     */
    public void setRequiredType(Class<T> requiredType) {
        this.requiredType = requiredType;
    }
    /**
     * Extract a value for the single column in the current row.
     * <p>Validates that there is only one column selected,
     * then delegates to <code>getColumnValue()</code> and also
     * <code>convertValueToRequiredType</code>, if necessary.
     * @see java.sql.ResultSetMetaData#getColumnCount()
     * @see #getColumnValue(java.sql.ResultSet, int, Class)
     * @see #convertValueToRequiredType(Object, Class)
     */
    public T mapRow(ResultSet rs, int rowNum) throws SQLException {
        // Validate column count.
        ResultSetMetaData rsmd = rs.getMetaData();
        int nrOfColumns = rsmd.getColumnCount();
        if (nrOfColumns != 1) {
            throw new InvalidDataAccessException("Incorrect column count: expected 1, actual " + nrOfColumns);
        }
        // Extract column value from JDBC ResultSet.
        Object result = getColumnValue(rs, 1, this.requiredType);
        if (result != null && this.requiredType != null && !this.requiredType.isInstance(result)) {
            // Extracted value does not match already: try to convert it.
            try {
                return (T) convertValueToRequiredType(result, this.requiredType);
            } catch (IllegalArgumentException ex) {
                throw new TypeMismatchDataAccessException("Type mismatch affecting row number " + rowNum + " and column type '" + rsmd.getColumnTypeName(1) + "': " + ex.getMessage());
            }
        }
        return (T) result;
    }
    /**
     * Retrieve a JDBC object value for the specified column.
     * <p>The default implementation calls
     * {@link JdbcUtils#getResultSetValue(java.sql.ResultSet, int, Class)}.
     * If no required type has been specified, this method delegates to
     * <code>getColumnValue(rs, index)</code>, which basically calls
     * <code>ResultSet.getObject(index)</code> but applies some additional
     * default conversion to appropriate value types.
     * @param rs is the ResultSet holding the data
     * @param index is the column index
     * @param requiredType the type that each result object is expected to match
     * (or <code>null</code> if none specified)
     * @return the Object value
     * @throws SQLException in case of extraction failure
     * @see net.hasor.jdbc.jdbc.core.util.support.noe.platform.modules.db.jdbcorm.jdbc.support.JdbcUtils#getResultSetValue(java.sql.ResultSet, int, Class)
     * @see #getColumnValue(java.sql.ResultSet, int)
     */
    protected Object getColumnValue(ResultSet rs, int index, Class requiredType) throws SQLException {
        if (requiredType != null) {
            return JdbcUtils.getResultSetValue(rs, index, requiredType);
        } else {
            // No required type specified -> perform default extraction.
            return getColumnValue(rs, index);
        }
    }
    /**
     * Retrieve a JDBC object value for the specified column, using the most
     * appropriate value type. Called if no required type has been specified.
     * <p>The default implementation delegates to <code>JdbcUtils.getResultSetValue()</code>,
     * which uses the <code>ResultSet.getObject(index)</code> method. Additionally,
     * it includes a "hack" to get around Oracle returning a non-standard object for
     * their TIMESTAMP datatype. See the <code>JdbcUtils#getResultSetValue()</code>
     * javadoc for details.
     * @param rs is the ResultSet holding the data
     * @param index is the column index
     * @return the Object value
     * @throws SQLException in case of extraction failure
     * @see net.hasor.jdbc.jdbc.core.util.support.noe.platform.modules.db.jdbcorm.jdbc.support.JdbcUtils#getResultSetValue(java.sql.ResultSet, int)
     */
    protected Object getColumnValue(ResultSet rs, int index) throws SQLException {
        return JdbcUtils.getResultSetValue(rs, index);
    }
    /**
     * Convert the given column value to the specified required type.
     * Only called if the extracted column value does not match already.
     * <p>If the required type is String, the value will simply get stringified
     * via <code>toString()</code>. In case of a Number, the value will be
     * converted into a Number, either through number conversion or through
     * String parsing (depending on the value type).
     * @param value the column value as extracted from <code>getColumnValue()</code>
     * (never <code>null</code>)
     * @param requiredType the type that each result object is expected to match
     * (never <code>null</code>)
     * @return the converted value
     * @see #getColumnValue(java.sql.ResultSet, int, Class)
     */
    protected Object convertValueToRequiredType(Object value, Class requiredType) {
        if (String.class.equals(requiredType)) {
            return value.toString();
        } else if (Number.class.isAssignableFrom(requiredType)) {
            if (value instanceof Number) {
                // Convert original Number to target Number class.
                return NumberUtils.convertNumberToTargetClass(((Number) value), requiredType);
            } else {
                // Convert stringified value to target Number class.
                return NumberUtils.parseNumber(value.toString(), requiredType);
            }
        } else {
            throw new IllegalArgumentException("Value [" + value + "] is of type [" + value.getClass().getName() + "] and cannot be converted to required type [" + requiredType.getName() + "]");
        }
    }
}